Communication DC power supply is widely used in communication areas such as a variety of switching equipment, microwave communication, mobile base stations and optical fiber transmission, and it is the “heart” of communication equipment and has a very important position in the communication network. Once the power system fails and causes the traffic to disrupt, it will cause huge economic losses and social impacts, therefore, the reliability of the power supply system is particularly important, wherein, the battery acts as a backup power supply, in case that AC power is in outage, the battery can still provide uninterruptible power supply for the communications equipment. With the rapid development of the telecommunications industry in recent years, the established trunk cable, microwave unmanned stations, and mobile base stations use a lot of batteries. Therefore, the battery management is an important function of the power supply system, and the reliability and improvement of the battery maintenance and management is also the top priority of the design.
The batteries currently used in the communication industry are mostly VRLA (valve regulated lead-acid) batteries, in order to ensure that the batteries are not over-discharged, all the power supply systems have under-voltage protection capability, that is, a battery voltage protection threshold is set, and when the battery voltage drops to the protection voltage, the power supply of the battery is cut off. Generally, according to the importance of the communication equipment, the power supply system has the capability of two power-downs, in particular, when the AC power is interrupted, the battery is used to supply power to the loads, when the battery discharges to a certain extent, in order to ensure the power supply of the primary loads, it needs to automatically disconnect the secondary loads, so that the battery only supplies power to the primary loads, which is the first power-down; when the battery continues to discharge and reaches the protection point, the power supply circuit of the battery to the primary loads is cut off, which is the second power-down. Two power-downs can effectively extend the time length of supplying power to the primary loads, and protect the battery from damaging due to over-discharge at the same time. There are two methods for two power-downs in the Communication DC Power System: in the first method, the first power-down makes the secondary loads disconnect, and second power-down makes the primary loads disconnect, and this method makes the loads disconnect from the power supply circuit; and in the second method, first power-down makes the secondary loads disconnect, and the second power-down makes the battery disconnect, and this method remove the battery from the power supply circuit. Compared with the first method, in the second method, the primary loads always connect with the power supply circuit, so there is a certain risk-resistant ability for the wrong power-downs. The two methods are both based on protection philosophy of VRLA battery as well as battery discharge management. With the development of science and technology and the advance of electrochemical materials and process technology, many new batteries, such as lithium iron phosphate, etc., begin to enter the field of communication, and compared with lead-acid batteries, these batteries are not suitable to connect with the power supply system and stay in a state of long-term online floating charge after they are fully-charged, which makes the battery life shortened, therefore, the protections of these new batteries are different from the lead-acid batteries, and the current two power-down methods can not meet the protection needs of the new batteries.